Monocytes have been found to directly stimulate bone resorption in vitro. Organ and cell culture methods will be used to investigate the mechanism of monocyte-related bone resorption and the effects of factors which stimulate and inhibit monocyte activity on this process. Monocytes will be cultured with bones for extended periods to determine if they are transformed into osteoclast-like bone resorbing cells. Bone will be examined to see if bone products exert any chemotactic influence on monocytes or isolated bone cells. The role of cell fusion in the formation of bone resorbing cells will be studied using artificial fusogens such as polyethylene glycol. The role of the microtubule-tubulin system in monocytes and isolated bone cells will be studied using colchicine and recently developed immunofluorescent antibodies against microtubules and tubulin.